Perhaps a large round table might mean a rug is not at all necessary. It could be a metal tray table, or carved wood like Rebecca Mitchell Interiors illustrates. Ideas also to consider, using multiple tables can be found at http://www.houzz.com/multiple-coffee-tables. I also agree with comments above that some color is needed on the walls. You could then hang round mirrors, or an unusual curved shape like RMI shows above.

Got it - if that works... I sort of like the idea of an art gallery being a journey of discovery so I created more corners and alleys for people to walk around.. in your case, the view would be easy to see everything in one swoop (but therefore not allow each piece of art to showcase itself uniquely)if you go back to my image, you have pictures leaning or hanging low on the floor level, you then have others higher up with jutting out shelves on which you have placed sculptures.The visitor walks around the block to find hidden artwork - they then walk up the block and view items displayed there (maybe a table with smaller sculptures and more artwork leaning on the balcony. They can then look out at the artwork on the walls and down on the artwork leaning on the floor on the lower level.... different vantage points: a journey.

If you want to highlight the staircase wall then your could use earthy colours such as a yellow ochre! The wall could be enhanced even more by using suitable frames and making a good collage composition for all the photos that you have (I can see many lying on the dining table). This colour would match well with wooden furnitures

You don't necessarily need only paintings as artwork. You can put some floating shelves near the dining space with some good crockery like plates or tea sets which can be used for occasions as well. On the wall in the living space you could keep either traditional or modern show pieces.